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991.
新型气动溢流阀及其动态特性的仿真分析 总被引:3,自引:0,他引:3
本文在介绍一种新型气动溢流阀的基础上,运用计算机仿真技术研究该阀的动态特性,建立了气动溢流阀的基本动态微分方程,采用数值方法求解方程,并把仿真结果用于指导气动溢流阀的设计,得到了满意的效果。 相似文献
992.
Babur Ozcelik Mahmut Bayramoglu 《International Journal of Machine Tools and Manufacture》2006,46(12-13):1395-1402
Surface roughness is one of the most important requirements in machining process. The surface roughness value is a result of the tool wear. When tool wear increase, the surface roughness also increases. The determination of the sufficient cutting parameters is a very important process obtained by means of both minimum surface roughness values and long tool life. The statistical models were developed to predict the surface roughness.This paper presents the development of a statistical model for surface roughness estimation in a high-speed flat end milling process under wet cutting conditions, using machining variables such as spindle speed, feed rate, depth of cut, and step over. First- and second-order models were developed using experimental results of a rotatable central composite design, and assessed by means of various statistical tests. The highest coefficient of correlation (Radj2) (88%) was obtained with a 10-parameter second-order model. Meanwhile, a time trend was observed in residual values between model predictions and experimental data, reflecting the probable effect of the tool wear on surface roughness. Thus, in order to enhance the estimation capability of the model, another independent variable was included into the model to account for the effect of the tool wear, and the total operating time of the tool was selected as the most suitable variable for this purpose. By inserting this new variable as a linear term into the model, Radj2 was increased to 94% and a good fit was observed between the model predictions and supplementary experimental data.In this study, it was observed that, the order of significance of the main variables is as X5>X3>X4>X1>X2 (total machining time, depth of cut, step over, spindle speed and feed rate, respectively). 相似文献
993.
994.
美国大学教学评估及其对中国高等教育的启示 总被引:4,自引:0,他引:4
美国大学和学院,学生对教师教学进行有效性评估。不同大学对教学有不同要求和标准;美国学术界对教学评估体系利与弊展开过辩论,而学生和老师的背景特征可能引起偏见。美国学生对老师进行教学评估的体系,对中国高等教育教学可能有一定的他石意义,但是,评估体系的现实条件有差异,中国不应当照抄或照搬美国教学评估,尤其应该摒弃将教与学关系扭曲为买方和卖方关系的观念。取其精华而弃其糟粕,建立适应中国的教学评估体系才能提高高等教育质量。 相似文献
995.
996.
连铸中间包内三维湍流流动的数值模拟 总被引:11,自引:0,他引:11
连铸中间包的操作条件决定了其内流动现象的复杂性,为此,本文选择两种不同的湍流模型k-ε和LES(Largeeddysimulation),建立了描述连铸中间包内三维湍流流动的数学模型,并实施了数值计算和模型验证,对单流中间包内的流动现象进行了描述,考察了有,无流动控制情况下中间包内的流动特征和湍流模型的合理性,结果表明,合理的流动控制有利于中间包内非金属夹杂的上浮和吸附,用k-ε模型基本上能够描述 相似文献
997.
方柱体镦粗的两个新力学模型 总被引:8,自引:1,他引:8
在对平板间镦粗圆柱体的研究[1,2,3]基础上,进一步对普通平板间的方柱体镦粗,进行了工程力学的分析,提出了二个新力学模型,并进行了实验验证。这为形成新的拔长理论[4,6]奠定了力学基础。 相似文献
998.
应用人工神经网络理论建立热粘塑性材料的本构关系 总被引:2,自引:1,他引:2
本文将人工神经网络(ANN)用于建立热粘塑性材料的本构关系,意在探索出一种描述材料变形力学行为的新方法。文中给出了应用人工神经网络建立热粘塑性材料本构关系的BP模型和学习算法过程,并应用于45号钢在高温和高速变形条件下的流动应力计算。计算结果与实测结果比较表明,二者吻合良好。因此,应用人工神经网络建立热粘塑性材料的本构关系具有重要的工程应用价值。 相似文献
999.
Marta Teixeira Pinto Ana Sofia Ribeiro Inês Conde Rita Carvalho Joana Paredes 《International journal of molecular sciences》2021,22(1)
The high plasticity of cancer stem-like cells (CSCs) allows them to differentiate and proliferate, specifically when xenotransplanted subcutaneously into immunocompromised mice. CSCs are highly tumorigenic, even when inoculated in small numbers. Thus, in vivo limiting dilution assays (LDA) in mice are the current gold standard method to evaluate CSC enrichment and activity. The chick embryo chorioallantoic membrane (CAM) is a low cost, naturally immune-incompetent and reproducible model widely used to evaluate the spontaneous growth of human tumor cells. Here, we established a CAM-LDA assay able to rapidly reproduce tumor specificities—in particular, the ability of the small population of CSCs to form tumors. We used a panel of organotropic metastatic breast cancer cells, which show an enrichment in a stem cell gene signature, enhanced CD44+/CD24−/low cell surface expression and increased mammosphere-forming efficiency (MFE). The size of CAM-xenografted tumors correlate with the number of inoculated cancer cells, following mice xenograft growth pattern. CAM and mice tumors are histologically comparable, displaying both breast CSC markers CD44 and CD49f. Therefore, we propose a new tool for studying CSC prevalence and function—the chick CAM-LDA—a model with easy handling, accessibility, rapid growth and the absence of ethical and regulatory constraints. 相似文献
1000.
Equivalent model of multi-type distributed generators under faults with fast-iterative calculation method based on improved PSO algorithm
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Puyu Wang Jinyuan Song Fangyu Liang Fang Shi Xiangping Kong Guangen Xie Xiao-Ping Zhang Xinxin Gu 《电力系统保护与控制》2021,6(3):371-382
There are various types of distributed generators (DGs) with diferent grid integration strategies. The transient char?
acteristics of the fault currents provided by the DGs are diferent to those of conventional synchronous generators. In
this paper, a distribution network with multi-type DGs is investigated, including consideration of DG low-voltage ride
through (LVRT). The fault current characteristics of two typical DGs, i.e. an inverter-interfaced distributed generator
(IIDG) and a doubly-fed induction generator (DFIG), are analyzed, considering the specifc operation modes. Based on
analysis of the fault characteristics, an equivalent model of the multi-type DGs under symmetrical/asymmetrical fault
conditions is established. A fast-iterative fault calculation method for enhancing the calculation efciency while avoid?
ing local convergence is then proposed using an improved particle swarm optimization (PSO) algorithm. A simula?
tion system of the distribution network with multi-type DGs is established in PSCAD/EMTDC. The simulation results
validate the high accuracy and calculation efciency of the proposed calculation method of the fault components.
This can assist in the settings of the protection threshold. 相似文献